Elastic properties of muscle-tendon complex in long-distance runners

The purpose of this study was to investigate the elastic properties of muscle-tendon complex (MTC) in knee extensor muscles and the capacity for elastic energy utilization in long-distance runners (LDR) by comparing with data obtained from untrained individuals (CON). The elongation (L) of the tendon and aponeurosis of vastus lateralis muscle during isometric knee extension was determined by real-time brightness mode ultrasonography, while the subjects developed a gradually increasing torque from 0 (relaxed) to maximal effort (MVC) within 7 s. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The relationship between L muscle and force (F ) was curvilinear and consisted of an initial region (toe region), characterized by a large increase in L with increasing F, immediately followed by a linear region. The slope of the regression equation for the L-F relationship in the range 50%–100% of MVC was defined as an index of MTC compliance, where the rate of the changes in L to that in muscle F at every 10% of MVC became almost constant. The maximal L (L _max) and MTC compliance were significantly lower in LDR than in CON: 29.9 (SD 3.9) mm in LDR compared to 33.3 (SD 5.5) mm in CON for L _max and 1.55 (SD 0.25) × 10⁻² mm · N⁻¹ in LDR compared to 1.88 (SD 0.82) × 10⁻² mm · N⁻¹ in CON for MTC compliance. Also, LDR showed significantly less elastic energy absorption (E _e) than CON, defined as the area below the L-F relationship curve from 0 to 100% of MVC. Not only jump heights but also the differences between the heights in SJ and CMJ, expressed as the percentage of the height in SJ, were significantly lower in LDR than in CON. The augmentation with counter-movement was significantly correlated to either MTC compliance (r = 0.554, P < 0.05) or E _e (r = 0.563, P < 0.05). Thus, the present results would indicate that MTC of vastus lateralis muscle is less compliant and its potential for energy storage during MTS lengthening is lower in LDR than untrained individuals. These elastic profiles of vastus lateralis muscle in LDR may be associated with their lower performances during CMJ. Accepted: 3 September 1999     

Estimation of extracellular space and blood volume using bioelectrical impedance measurements

Summary The bromide-82 dilution space (extracellular space, ECS) and blood volume (BV) were measured in 21 patients with esophageal and gastric cancer and in 27 patients 18–96 months after total gastrectomy. Resistance (R) and reactance (X_c) from bioelectrical impedance measurements were used to obtain multiple regression equations for ECS and BV. The variables weight, gender, and height ²/X_c were independent predictors of ECS (r = 0.767; P < 0.0001). Height 2/R and gender were predictors of blood volume (r = 0.856; P < 0.0001). The mean difference between the Br space and the ECS predicted from impedance measurements was 0 ± 1.54 (mean ± SD). The limits of agreement (± 2 SD) were therefore ±3.081 or 19.6% of the mean Br space of 15.71. The limits of agreement for BV were ±789 ml or ±19.7% of the average BV of 4008 ml. It is concluded that bioelectrical impedance plethysmography using a single frequency can be used for the estimation of ECS and BV The wide limits of agreement, however, may limit its used in clinical practice.Abbreviations ECS extracellular space - BV blood volume - R resistance - X_c reactance - SD standard deviation - LBM lean body mass - TBW total body water - RCM red blood cell mass - cAMA corrected arm muscle area - Z impedance - ANOVA analysis of variance - NS not significant - Na_e/K_c exchangeable sodium to exchangeable potassium ratio - p specific resistivity - PV plasma volume     

Linear-lumped-parameter modeling of pulmonary impedance in monkeys

Pulmonary impedance, Z_L, measured from 2 to 32 Hz in anesthetized, intubated and paralyzed bonnet monkeys (Macaca radiata) was fitted to a variety of linearlumped parameter mechanical networks. Parameter values for each network were obtained by minimizing the average of the percent distance, D_r, between the computed network impedance and measured Z_L at all frequencies. Measured resistance, R_L, decreased from 2 to 8 Hz and increased from 8 to 32 Hz indicating that a single series resistance-inertance-compliance (RIC) network was not optimal (D_r∼19%). Networks consisting of two series RIC pathways in parallel resulted in a lower D_r (∼14%), but parameter values were difficult to interpret. Despite not modeling the decrease in R_L with frequency below 8 Hz, an airway wall compliance, C _aw , network in which the airways were separated into central and peripheral components resulted in an even lower D_r (∼11%). In addition, parameter values were easy to interpret, consistent among our “normal” monkeys and changed consistently and explainably with change in lung mechanics induced by decrease in lung volume. We conclude that (1) networks containing both parallel pathways and C _aw are necessary to model Z_L over the entire frequency range (2–32 Hz), (2) the effect of C _aw is an important determinant of Z_L above 8 Hz, and (3) a six-parameter C _aw network with the ratio of C _aw to parenchymal compliance, C_p, fixed may prove useful in interpreting changes in Z_L induced by alterations in lung mechanics in monkeys.     

Distal colonic Na+ absorption inhibited by luminal P2Y2 receptors

Luminal P2 receptors are ubiquitously expressed in transporting epithelia. In steroid-sensitive epithelia (e.g., lung, distal nephron) epithelial Na⁺ channel (ENaC)-mediated Na⁺ absorption is inhibited via luminal P2 receptors. In distal mouse colon, we have identified that both, a luminal P2Y₂ and a luminal P2Y₄ receptor, stimulate K⁺ secretion. In this study, we investigate the effect of luminal adenosine triphosphate/uridine triphosphate (ATP/UTP) on electrogenic Na⁺ absorption in distal colonic mucosa of mice treated on a low Na⁺ diet for more than 2 weeks. Transepithelial electrical parameters were recorded in an Ussing chamber. Baseline parameters: transepithelial voltage (V _te): −13.7 ± 1.9 mV (lumen negative), transepithelial resistance (R _te): 24.1 ± 1.8 Ω cm², equivalent short circuit current (I _sc): −563.9 ± 63.8 μA/cm² (n = 21). Amiloride completely inhibited I _sc to −0.5 ± 8.5 μA/cm². Luminal ATP induced a slowly on-setting and persistent inhibition of the amiloride-sensitive I _sc by 160.7 ± 29.7 μA/cm² (n = 12, NMRI mice). Luminal ATP and UTP were almost equipotent with IC₅₀ values of 10 μM and 3 μM respectively. In P2Y₂ knock-out (KO) mice, the effect of luminal UTP on amiloride-sensitve Na⁺ absorption was absent. In contrast, in P2Y₄ KO mice the inhibitory effect of luminal UTP on Na⁺ absorption remained present. Semiquantitative polymerase chain reaction did not indicate regulation of the P2Y receptors under low Na⁺ diet, but it revealed a pronounced axial expression of both receptors with highest abundance in surface epithelia. Thus, luminal P2Y₂ and P2Y₄ receptors and ENaC channels co-localize in surface epithelium. Intriguingly, only the stimulation of the P2Y₂ receptor mediates inhibition of electrogenic Na⁺ absorption.     

Attenuated β-adrenoceptor-mediated cardiac contractile responses following androgenic steroid administration to sedentary rats

Androgenic steroids administered in doses at pharmacological levels to sedentary animals have been shown to result in a reduced β-adrenoceptor-mediated increase in systolic cardiac performance when assessed in vivo. Whether the attenuated adrenergic response occurs as a consequence of alterations in either cardiac loads, heart rate, modifications in left ventricular (LV) geometry, or a decrease in myocardial contractile performance has not been determined. In this study the effect of chronic administration (over 3 months) of an androgenic steroid (nandrolone decanoate, 5 mg · kg⁻¹ biweekly) on the response of load-insensitive indices of myocardial contractile function [the slope of the LV systolic stress-strain relationship (LV-Eⁿ _max, where Eⁿ _max is systolic myocardial elastance)] to an adrenergic-inotropic stimulus was examined ex vivo in paced rat hearts. Systolic cardiac performance was assessed at 300 beats · min⁻¹ in isolated constant flow perfused heart preparations both before and during 10^−8.5 mol · l⁻¹ isoproterenol (ISO) infusion (approximate concentration of ISO eliciting 50% maximal inotropic response to ISO). Steroid administration resulted in left-shifted LV systolic and diastolic pressure-volume (P-V ) relationships. The leftshifted P-V relationships were attributed, in part, to increased slopes of these relationships. However, the steroid-mediated increment in the slope of the systolic P-V relationship (systolic chamber elastance, E_max) was not associated with a similar change in LV Eⁿ _max [control 19.2 (SEM 2.1) g · cm⁻², steroid 18.3 (SEM 2.4) g . cm⁻²] as determined in the absence of ISO. Isoproterenol infusion resulted in an increase in both E_max and Eⁿ _max in the control rats, without altering systolic performance in the steroid treated rats. Consequently, in the presence of ISO, the steroid treated rats exhibited a similar E_max, but a reduction in Eⁿ _max compared to the control rats [control 25.6 (SEM 1.9) g · cm⁻², steroid 18.5 (SEM 1.5) g · cm⁻²; P < 0.05]. In conclusion, these results would suggest that chronic high dose androgenic steroid administration produces a decrease in myocardial contractile reserve to β-adrenoceptor stimulation. Accepted: 3 September 1999     

Laboratory evaluation of traditionally used plant-based insect repellent against the malaria vector Anopheles arabiensis Patton (Diptera: Culicidae)

A laboratory study was carried out to evaluate the repellent efficacy of a methanol-leaf extract of Ethiopian traditionally used insect repellent plant viz., Lomi sar [vernacular name (local native language, Amharic); Cymbopogon citratus (DC) Stapf. (Poaceae)] against Anopheles arabiensis at four different concentrations viz., 1.0, 1.5, 2.0, and 2.5 mg/cm². The percentage protection in relation to the dose method was performed. C. citratus extract has shown various degrees of repellency impact against A. arabiensis. It provided the maximum total percentage protection of 78.83% at 2.5 mg/cm² and followed 68.06% at 2.0 mg/cm² for 12 h. All four tested concentrations of C. citratus extract offered significant protection and Student's t test results shows statistically significant (p value = 0.001) [1.0 mg/cm² (t = 22.89; df = 4); 1.5 mg/cm² (t = 24.03; df = 4); 2.0 mg/cm² (t = 36.92; df = 4); 2.5 mg/cm² (t = 22.31; df = 4)] difference between treated and control groups. The result suggests that it could serve as a potent insect repellent against vectors of disease. Globally, C. citratus is renowned for its therapeutic values. Above and beyond, due to its user- as well as environmental-friendly nature, it should be promoted among the marginalized populations in order to reduce man-vector contact. In addition, this appropriate strategy affords the opportunity to minimize chemical repellent usage and the risks associated with adverse side effects. At the end of the day, traditionally used plant-based insect repellents could be viable safer alternative sources for chemical insect repellents.     

Early Left Ventricular Diastolic Function Quantitation Using Directional Impedances

Impedance has been used in vascular biology to characterize the frequency dependent opposition the circulatory system presents to blood flow in response to a pulsatile pressure gradient. It has also been used to characterize diastolic function (DF) via the early, diastolic left ventricular (LV) pressure–flow relation. In a normal LV, early filling volume is accommodated primarily by wall-thinning and ascent of the mitral annulus relative to the spatially fixed apex (longitudinal chamber expansion). Simultaneously, the endocardial (transverse or short axis) dimension also increases while epicardial (transverse) external dimension remains essentially constant. To quantify these directional filling attributes, we compute longitudinal (Z _L) and transverse (Z _T) impedances during early rapid-filling (Doppler E-wave). Z _L and Z _T were calculated from 578 cardiac cycles of simultaneous transmitral flow and high fidelity LV pressure data in 17 subjects with normal LV function. Average Z _L was 0.7 ± 0.4 mmHg s/cm⁴ and average Z _T was 238 ± 316 mmHg s/cm². Direct comparison, in the same units is achieved by computing Z _T over the ≈10 cm² cross-sectional area of LV (denoted ?_T) revealing that Z _L is ≈34 times smaller than ?_T. This quantifies the physiologic preference for longitudinal LV volume accommodation. Lowest Z _L and Z _T values occurred in the first harmonic with monotonically increasing values with higher harmonics. We conclude that Z _L and Z _T characterize longitudinal and transverse chamber properties of DF and therefore, diastolic dysfunction can be viewed as a state of impedance mismatch.     

Development of an equation to predict muscle volume of elbow flexors for men and women with a wide range of age

The present study examined the age-related changes in muscle thickness (MT) and volume (MV) of elbow flexors and developed a prediction equation of the MV based on the MT applicable to men and women with a wide range of age. The MT and MV were determined from a single ultrasonographic image and multiple magnetic resonance imaging scans, respectively, in 72 men and 75 women aged 19–77 year. As a result of examining the age-MT and age-MV relationships by calculation of partial correlation coefficients with the control variable of gender, MV was decreased with aging whereas the corresponding decline in MT was not significant. The subjects were randomly separated into either a validation (38 men and 42 women) or a cross-validation (34 men and 33 women) group, and a multiple regression equation to estimate MV using not only MT but also upper arm length (L), age and gender as independent variables [MV (cm³) = 60.8 × MT (cm) + 6.48 × L (cm) − 0.709 × age (year) + 51.4 × gender (0 women, 1 men) − 187.4] was validated and cross-validated. Thus, the prediction equation for MV of elbow flexors newly developed was shown to be applicable to men and women with a wide range of age.     

Benefit of endurance training in elderly people over a short period is reversible

 The present study assessed daily activity, physical capacity and body composition in 11 initially sedentary healthy subjects [5 men and 6 women, mean age 62.8 (SD 2.7) years] before training (T_o), after completion of 7 (T_7w) and 14 (T_14w) weeks of training, and again 6 (T_6m) and 12 (T_12m) months after training. The mean daily activity index decreased from T_7w to T_12m reaching a lower level than at T_o [T_12m − T_o = −1.5 (SD 4.6) units, P = 0.18]. Mean maximal oxygen uptake (V˙O_2max) and its corresponding mean power output (W˙ _max) were increased by 12.5 (SD 6.6)% (P = 0.003) and 22.8 (SD 12.8)% (P = 0.003), respectively, at T_14w, and returned to their T_o levels within 1 year. Mean body mass (m _b) remained stable until T_6m but increased significantly by 2.6 (SD 3.7)% from T_6m to T_12m (P < 0.05). Mean fat mass (m _f, from bioelectrical impedance analysis measurements) tended to decrease [−2.0 (SD 4.2)%, P = 0.10] during the training period but increased by 7.8 (SD 10.9)% between T_6m and T_12m (P < 0.05). The mean fat free mass did not vary during the study period (P = 0.81) but magnetic resonance imaging (MRI) showed that mean thigh muscle volume decreased between T_7w and T_12m to less than at T_o [T_12m − T_o = −2.3 (SD 3.6)%, P = 0.05]. Therefore, this study confirmed the favourable effects of endurance training on the physical capacity and body composition of elderly people, but demonstrated that the training programme would have to be continued to maintain the training-related benefits (i.e. increased V˙O_2max and W˙ _max) which would otherwise be lost within 1 year. After training, m _b and m _f were found to be increased. Furthermore, a fast and reproducible MRI protocol was validated for study of small intra-individual variations in tissue volumes in longitudinal studies. Accepted: 7 September 1999     

A new impedance cardiograph device for the non-invasive evaluation of cardiac output at rest and during exercise: comparison with the “direct” Fick method

The objectives of this study were to evaluate the reliability and accuracy of a new impedance cardiograph device, the Physio Flow, at rest and during a steady-state dynamic leg exercise (work intensity ranging from 10 to 50 W) performed in the supine position. We compared cardiac output determined simultaneously by two methods, the Physio Flow (Q˙ _cPF) and the direct Fick (Q˙ _cFick) methods. Forty patients referred for right cardiac catheterisation, 14 with sleep apnoea syndrome and 26 with chronic obstructive pulmonary disease, took part in this study. The subjects' oxygen consumption values ranged from 0.14 to 1.19 l · min⁻¹. The mean difference between the two methods (Q˙ _cFick−Q˙ _cPF) was 0.04 l · min⁻¹ at rest and 0.29 l · min⁻¹ during exercise. The limits of agreement, defined as mean difference ± 2SD, were −1.34, +1.41 l · min⁻¹ at rest and −2.34, +2.92 l · min⁻¹ during exercise. The difference between the two methods exceeded 20% in only 2.5% of the cases at rest, and 9.3% of the cases during exercise. Thoracic hyperinflation did not alter Q˙ _cPF. We conclude that the Physio Flow provides a clinically acceptable and non-invasive evaluation of cardiac output under these conditions. This new impedance cardiograph device deserves further study using other populations and situations. Accepted: 3 April 2000     

Influence of ultra-long-term fatigue on the oxygen cost of two types of locomotion

The aim of this study was to examine the effects of fatigue induced by a 65-km ultramarathon on the oxygen cost of running (C_r) and cycling (C_cycl). The day before and immediately after the race, a group of nine well-trained male subjects performed two sub-maximal 4-min exercise bouts: one cycling at a power corresponding to 1.5 W · kg⁻¹ body mass on an electromagnetically braked ergometer, and one running at 11 km · h⁻¹ on a flat asphalt roadway. Before oxygen cost determinations, the subjects performed 12 “ankle” jumps at a given frequency that was fixed by an electronic metronome (2.5 Hz). From the non-fatigued to the fatigued condition, there was a significant increase in minute ventilation for both running (P < 0.01) and cycling (P < 0.0001). Significant changes were also found in respiratory exchange ratio both for running (P=0.01) and cycling (P < 0.0001). However, running and cycling differed in that C_cycl increased significantly by [mean (SD)] 24.2 (11.5)% (P < 0.001), suggesting an alteration of muscle efficiency, while C_r did not change with fatigue [186.8 (14.1) mlO₂ · kg⁻¹ · km⁻¹ vs 186.8 (18.7) mlO₂ · kg⁻¹ · km⁻¹]. In addition, contact times during hopping increased significantly from 0.173 (0.019) ms to 0.194 (0.027) ms (P < 0.01). Analysis of the factors that determine C_r indicate that the subjects modified their movement pattern in order to decrease the mechanical cost of running in such long-term fatigue conditions. Accepted: 7 August 2000     

Ryanoids change the permeability of potassium channels of locust (Schistocerca gregaria) muscle

The plasma membrane of locust skeletal muscle contains two types of K⁺ channel; a maxi, Ca²⁺-activated 170 pS channel (BK channel) and an inward rectifier of 35 pS conductance (IK channel). The effects of ryanodine, 9, 21-didehydroryanodine and 9, 21-didehydroryanodol on these channels have been investigated. In the concentration domain 10⁻⁹ M to 10⁻⁵ M, ryanodine irreversibly induced a dose-dependent reduction of the reversal potential (V _rev) of the channel currents, measured under physiologically normal K⁺ and Na⁺ gradients, i.e. from ≈60 mV in the absence of ryanodine to ≈15 mV for 10⁻⁵ M ryanodine. The alteration of K⁺ channel selectivity was Ca²⁺ independent. 9, 21-Didehydroryanodine and 9, 21-didehydroryanodol reduced V _rev, but only to ≈35 mV during application of 10⁻⁵ M of these compounds. 9, 21-Didehydroryanodine also diminished the conductances of the locust K⁺ channels. The three ryanoids reduced V _rev of a Ca²⁺-activated, high-conductance channel in inside-out patches excised from mouse interosseal muscle, although the changes were in each case less pronounced than those for the locust K⁺ channels. Also, the action of 9, 21-didehydroryanodine on mouse K⁺ (BK) channels was restricted to a shift of V _rev. For all three ryanoids, the IC₅₀ coefficients (i.e. the concentration of toxin that gave a 50% reduction in V _rev) for the shifts in V _rev were similar for the locust and mouse muscle K⁺ channels. Received: 12 June 1995/Received after revision and accepted: 30 January 1996     

Effect of strenuous strength training on the Na-K pump concentration in skeletal muscle of well-trained men

This study examined how strenuous strength training affected the Na-K pump concentration in the knee extensor muscle of well-trained men and whether leg muscle strength and endurance was related to the pump concentration. First, the pump concentration, taken as ³H-ouabain binding, was measured in top alpine skiers since strength training is important to them. Second, well-trained subjects carried out strenuous eccentric resistance training either 1, 2, or 3 times · week⁻¹ for 3 months. The Na-K pump concentration, the maximal muscle strength in a full squat lift (one repetition maximum, 1 RM), and the muscle endurance, taken as the number of full squat lifts of a mass of 70% of the 1 RM load, were measured before and after the training period. The mean pump concentration of the alpine skiers was 425 (SEM 11) nmol · kg⁻¹ wet muscle mass. The subjects in part two increased their maximal strength in a dose-dependent manner. The muscle endurance increased for all subjects but independently of the training programme. From a mean starting value of 356 (SEM 6) nmol · kg⁻¹ the mean Na-K pump concentration increased by 54 (SEM 15) nmol · kg⁻¹ (+15%, P < 0.001) when the results for all subjects were pooled. The effect was larger for those who had trained twice a week than for those who had trained only once a week (P=0.025), suggesting that the effect of strength training depended on the amount of training carried out. The muscle strength and endurance were not related to the pump concentration, suggesting that the pumping power of this enzyme did not limit the performance during heavy lifting. However, the individual improvements in the endurance test during the training period correlated with the individual changes in the pump concentration (r _Spearman=0.5; P=0.01) which could mean that a common factor both increases the pump concentration and makes the muscles more adapted to repeated heavy lifting. Accepted: 8 August 2000     

Augmentation of blood circulation to the fingers by warming distant body areas

Future activities in space will require greater periods of time in extreme environments in which the body periphery will be vulnerable to chilling. Maintaining the hands and fingers in comfortable conditions enhances finger flexibility and dexterity, and thus effects better work performance. We have evaluated the efficacy of promoting heat transfer and release by the extremities by increasing the blood flow to the periphery from more distant parts of the body. The experimental garment paradigm developed by the investigators was used to manipulate the temperature of different body areas. Six subjects, two females and four males, were evaluated in a stage-1 baseline condition, with the inlet temperature of the circulating water in the liquid cooling/warming garment (LCWG) at 33 °C. At stage 2 the total LCWG water inlet temperature was cooled to 8 °C, and at stage 3 the inlet water temperature in specific segments of the LCWG was warmed (according to protocol) to 45 °C, while the inlet temperature in the rest of the LCWG was maintained at 8 °C. The following four body- area-warming conditions were studied in separate sessions: (1) head, (2) upper torso/arm, (3) upper torso/arm/head, and (4) legs/feet. Skin temperature, heat flux and blood perfusion of the fingers, and subjective perception of thermal sensations and overall physical comfort were assessed. Finger temperature (T _fing) analyses showed a statistically significant condition × stage interaction. Post-hoc comparisons (T _fing) indicated that at stage 3, the upper torso/arm/head warming condition was significantly different from the head, upper torso/arm and legs/feet conditions, showing an increase in T _fing. There was a significant increase in blood perfusion in the fingers at stage 3 in all conditions. Subjective perception of hand warmth, and overall physical comfort level significantly increased in the stage 3 upper torso/arm/head condition. The findings indicate that physiological methods to enhance heat transfer by the blood to the periphery within protective clothing provide an additional tool for increasing total and local human comfort in extreme environments. Accepted: 20 December 1999     

Cycling on Earth, in space, on the Moon

The mechanical power for cycling (P_c) at constant ground speed (s), in the absence of wind on smooth hard terrain is the sum of the power dissipated against rolling resistance, gravity and air resistance: P_c=a · s + M · g · s · sin γ + b · s ³, where a and b are constants, M is the mass of the subject plus bike, g is the acceleration of gravity and γ is the angle of the terrain with the horizontal. The constant b depends upon the drag coefficient (C_d), the overall area projected on the frontal plane (A _f), and the air density (ρ_a): b=0.5 · C_d · A _f · ρa. In turn, ρ_a depends on air pressure (P _B) and temperature (T): ρ_a=ρ₀ · 0.359 · P _B · T ⁻¹, where ρ₀ is the air density at 760 mmHg (101.3 kPa) and 273 K. The metabolic power developed by the cyclist (Ė _c) is related to P_c:Ė _c=P_c·η⁻¹, where η is the mechanical efficiency of cycling. The experimental values of a, b and η are fairly well known so that, if the maximal metabolic power as a function of the performance time is known for a given cyclist, the following set of data can be individually calculated: (1) best performances over any given distance and for any given altitude above sea level, (2) the effects of posture and body size on maximal speeds, and (3) the maximal incline of the terrain that can be overcome at any given speed or coasting speed for any given downslope. The above set of information makes it possible also to calculate the characteristics of a “Twin Bikes System” (TBS) for preventing microgravity deconditioning during long-term space flight. The TBS consists of two bicycles that are mechanically coupled by a differential gearing, which move at the very same speed, but in the opposite sense, along the inner wall of a cylindrically shaped space module. The circular trajectories induce a centrifugal acceleration vector (a _c) oriented along the head-to-feet direction of each subject: a _c=v _t ² · r ⁻¹ where v _t is the tangential velocity and r the radius of gyration, which is equal to the inner radius of the space module. So, any desired value of a _c can be achieved by appropriately selecting v _t, wherefrom the mechanical and metabolic powers that the astronauts must generate can be readily calculated. Experiments performed in a ground-based human centrifuge have shown that the discomfort derived from the rotating environment is reasonably low and well tolerated. If the appropriate atmospheric pressure is provided, cycling on circular or elliptical tracks may be useful to reduce cardiovascular deconditioning that occurs due to the reduced gravity in permanently manned lunar bases. Indeed, on the curved parts of the path a cyclist will generate a horizontal outward acceleration: a _c=s ² · r ⁻¹, where s is the velocity along the track and r is the radius of curvature. To counterbalance a _c, the subject plus bike must lean inwards so that the vectorial sum of a _c plus the lunar gravity (g _L=1.62 m · s⁻²) is applied along a straight line that includes the centre of mass of the system and the point of wheel contact with the ground. For values of s from 10 to 20 m · s⁻¹ and r from 50 to 200 m, this vectorial sum ranges from 1.05 to 5.03 g _L (0.17–0.83 g). Accepted: 20 March 2000     

Relationship between muscle T2 * relaxation properties and metabolic state: a combined localized 31P-spectroscopy and 1H-imaging study

A multi-volume ³¹P-magnetic resonance spectroscopy localization procedure was implemented to compare directly muscle metabolism and proton T₂ ^* relaxation properties in the human plantar flexor muscles during exercise. Localized ³¹P-spectra were collected simultaneously from the medial gastrocnemius, lateral gastrocnemius and soleus muscles during exercise using β ₁-insensitive Hadamard Spectroscopic Imaging (HSI). ¹H T₂ ^*-weighted gradient-echo images were acquired at rest and immediately following high-intensity plantar flexion exercise. T₂ ^* mapping of the individual calf muscles showed that plantar flexion with the knee extended produces significant increases (P < 0.0001) in the mean (SEM) T₂ ^* of the medial [35.6 (1.2) ms vs 28.5 (0.5) ms at rest] and lateral gastrocnemius [35.6 (0.9) ms vs 26.2 (0.9) ms at rest], but not in the soleus [26.7 (0.6) ms vs 27.3 (0.8) ms at rest]. In accordance with the changes in T₂ ^*, the ratio of inorganic phosphate to phosphocreatine (P_i:PCr) and the intracellular muscle pH shifted significantly in the gastrocnemii, while the soleus showed no change in muscle pH and only a moderate increase in P_i-to-Ph. Comparison of spectroscopic and relaxation parameters in both gastrocnemius muscles revealed a significant relationship between post-exercise T₂ ^* and intracellular pH (r=0.72–0.76) and P_i-to-Ph ratios (r=0.81–0.88) during exercise. Using an improved method of localization, this study confirms the existence of a strong relationship between transverse relaxation properties and the metabolic state in skeletal muscles engaged in heavy exercise. Accepted: 28 December 1999     

Muscle blood flow and flow heterogeneity during exercise studied with positron emission tomography in humans

Blood flow is the main regulator of skeletal muscle's oxygen supply, and several studies have shown heterogeneous blood flow among and within muscles. However, it remains unclear whether exercise changes the heterogeneity of flow in exercising human skeletal muscle. Muscle blood flow and spatial flow heterogeneity were measured simultaneously in exercising and in the contralateral resting quadriceps femoris (QF) muscle in eight healthy men using H¹⁵ ₂O and positron emission tomography. The relative dispersion (standard deviation/mean) of blood flow was calculated as an index of spatial flow heterogeneity. Average muscle blood flow in QF was 29 (10) ml · (kg muscle)⁻¹ · min⁻¹ at rest and 146 (54) ml · (kg muscle)⁻¹ · min⁻¹ during exercise (P=0.008 for the difference). Blood flow was significantly (P < 0.001) higher in the vastus medialis and the vastus intermedius than in the vastus lateralis and the rectus femoris, both in the resting and the exercising legs. Flow was more homogeneous in the exercising vastus medialis and more heterogeneous (P < 0.001) in the exercising vastus lateralis (P=0.01) than in the resting contralateral muscle. Flow was more homogeneous (P < 0.001) in those exercising muscles in which flow was highest (vastus intermedius and vastus medialis) as compared to muscles with the lowest flow (vastus lateralis and the rectus femoris). These data demonstrate that muscle blood flow varies among different muscles in humans both at rest and during exercise. Muscle perfusion is spatially heterogeneous at rest and during exercise, but responses to exercise are different depending on the muscle. Accepted: 16 June 2000     

Breathing pattern and exercise endurance time after exhausting cycling or breathing

The aim of the present study was to investigate whether the changes in breathing pattern that frequently occur towards the end of exhaustive exercise (i.e., increased breathing frequency, f _b, with or without decreased tidal volume) may be caused by the respiratory work itself rather than by leg muscle work. Eight healthy, trained subjects performed the following three sessions in random order: (A) two sequential cycling endurance tests at 78% peak O₂ consumption (V˙O_2peak) to exhaustion (A1, A2); (B) isolated, isocapnic hyperpnea (B1) at a minute ventilation (V˙ _E) and an exercise duration similar to that attained during a preliminary cycling endurance test at 78% V˙O_2peak, followed by a cycling endurance test at 78% V˙O_2peak (B2); (C) isolated, isocapnic hyperpnea (C1) at a V˙ _E at least 20% higher than that of the preliminary cycling test and the same exercise duration as the preliminary cycling test, followed by a cycling endurance test at 78% V˙O_2peak (C2). Neither of the two isocapnic hyperventilation tasks (B1 or C1) affected either the breathing pattern or the endurance times of the subsequent cycling tests. Only cycling test A2 was significantly shorter [mean (SD) 26.5 (8.3) min] than tests A1 [41.0 (9.0) min], B2 [41.9 (6.0) min], and C2 [42.0 (7.5) min]. In addition, compared to test A1, only the breathing pattern of test A2 was significantly different [i.e., V˙ _E: +10.5 (7.6) l min⁻¹, and f _b: +12.1 (8.5) breaths min⁻¹], in contrast to the breathing patterns of cycling tests B2 [V˙ _E: −2.5 (6.2) l min⁻¹, f _b: +0.2 (3.6) breaths min⁻¹] and C2 [V˙ _E: −3.0 (7.0) l min⁻¹, f _b: +0.6 (6.1) breaths min⁻¹]. In summary, these results suggest that the changes in breathing pattern that occur towards the end of an exhaustive exercise test are a result of changes in the leg muscles rather than in the respiratory muscles themselves. Accepted: 7 October 1999     

In vivo specific tension of the human quadriceps femoris muscle

It is not known to what extent the inter-individual variation in human muscle strength is explicable by differences in specific tension. To investigate this, a comprehensive approach was used to determine in vivo specific tension of the quadriceps femoris (QF) muscle (Method 1). Since this is a protracted technique, a simpler procedure was also developed to accurately estimate QF specific tension (Method 2). Method 1 comprised calculating patellar tendon force (F _t) in 27 young, untrained males, by correcting maximum voluntary contraction (MVC) for antagonist co-activation, voluntary activation and moment arm length. For each component muscle, the physiological cross-sectional area (PCSA) was calculated as volume divided by fascicle length during MVC. Dividing F _t by the sum of the four PCSAs (each multiplied by the cosine of its pennation angle during MVC) provided QF specific tension. Method 2 was a simplification of Method 1, where QF specific tension was estimated from a single anatomical CSA and vastus lateralis muscle geometry. Using Method 1, the variability in MVC (18%) and specific tension (16%) was similar. Specific tension from Method 1 (30 ± 5 N cm⁻²) was similar to and correlated with that of Method 2 (29 ± 5 N cm⁻²; R ² = 0.67; P < 0.05). In conclusion, most of the inter-individual variability in MVC torque remains largely unexplained. Furthermore, a simple method of estimating QF specific tension provided similar values to the comprehensive approach, thereby enabling accurate estimations of QF specific tension where time and resources are limited.     

Infestation status of gnathiid isopod juveniles parasitic on Dusky grouper (<Emphasis Type="Italic">Epinephelus marginatus</Emphasis>) from the northeast Mediterranean Sea

This is the first detailed documented record of Gnathiid isopod praniza larvae infestating dusky grouper, (Epinephelus marginatus Lowe 1834) in the northeast Mediterranean Sea (36°36′N–36°07′E, 35°52′N–36°25′E). Fish were sampled monthly from Iskenderun Bay during a 3-year period from 2000 to 2003 [N = 468, W ± SD (range) = 503.69 ± 342.35 g (177–2,832 g), TL ± SD (range) = 32.39 ± 9.22 cm (16.1–67.0 cm), W _total = 0.213L _total ^2.19, r _total ² = 0.85]. Juveniles of the Gnathia sp. were only extracted from the epithelium of the buccal cavity. The monthly and seasonal patterns in infestation rates (mean prevalence, P = 27.35% and mean intensity, MI ± SD = 21.35 ± 16.19), and the relationship between length–weight and infested/non-infested fish were calculated. This study suggests that gnathiid parasite has no effect on the growth and general health condition of infested fish, although high intensities were observed in fish.